1. Field of the Invention
This invention relates to improvements in rolling process and apparatus for producing gears to be used in a power transmitting mechanism and a transmission of automotive vehicles and a variety of industrial machines, and more particularly to the improvements in the rolling process and apparatus by which chamfered portions can be formed at the corner portions of each tooth of the gear simultaneously with production of the gear by rolling.
2. Description of the Prior Art
In the past chamfering of teeth of a gear has not been usually accomplished simultaneously with formation of the gear per se. Specifically, the gear per se is first produced by rolling or cutting using a gear-hobbing machine or a gear-shaping machine. Thereafter, corner portions of each tooth of the gear are chamfered by cutting or grinding. However, such chamfering by machining is complicated in operation and process thereby requiring a relatively long time for production of the gear while increasing production cost, particularly where the number of teeth in the gear is large.
Additionally, it has been proposed that portions for chamfering are formed at the opposite ends of the bottom land of gear teeth of a rolling tool so that chamfering at the opposite ends of each tooth of a gear to be produced is made simultaneously with rolling of the gear per se. This proposal is disclosed, for example, in Japanese Patent Publication No. 5-38667. However, the following difficulties have been encountered in this proposal: The rolling tool is complicated in shape owing to the portions for chamfering, and therefore a low-cost machining process such as wire cutting process cannot be used to produce the rolling tool for the gear. This not only increases production cost of the rolling tool, but also applies a high load to the rolling tool so that the rolling tool becomes heavily damaged to wear or the like. That is why the chamfering and the formation of the gear per se have been accomplished with the same tool. Otherwise, the above Japanese Patent Publication describes facilitating production of the rolling tool by dividing the rolling tool into a gear teeth formation section and a chamfering section. However, it is difficult to make a phase-mating between the gear teeth formation section and the chamfering section without producing burr at the parting portion between the sections.